Despite todays findings of toxic perchlorate in Martian soil, NASA is not ready to write off life on Mars; leading space scientists point to earthbound extremeophiles that process the substance.

Less than a week after NASA announced that its Phoenix Lander has positively identified water on Mars, the agency today dampened enthusiasm for the search for Martian life by announcing the probe has found a toxic chemical that is not friendly to life. Although media leaks of today's announcement started the buzz on indications that life could not exist on the planet, scientists inside and out of the Phoenix program hold out hope that Mars could still harbor organisms.

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NASA's announcement this afternoon detailed the presence of a highly oxidizing substance called perchlorate in the planet's soil­--making Martian life a long shot because the highly reactive salt would break down organic compounds. Samples of Martian soil containing perchlorate have been tested in two labs on the Phoenix Mars Lander: the Microscopy, Electrochemistry and Conductivity Analyzer (MECA) and the Thermal and Evolved-Gas Analyzer (TEGA). NASA is now ready to report the results from both machines.

The agency has said that it has no idea how perchlorate formed on Mars, and a possible (but unlikely) contamination from the probe is being examined. There is also confusion over conflicting findings from the lander: Preliminary Phoenix tests "suggested Earth-like soil. Further analysis has revealed non-Earth-like aspects of the soil chemistry," says Phoenix chief scientist Peter Smith. He also noted that organisms exist on Earth that can process the substance, so things now looked "neither good nor bad for life."

The presence of a highly oxidizing agent is not necessarily a death knell for prior life on Mars, some scientists say. In April's edition of the journal Astrobiology, researchers--including an investigator from NASA, Chris McKay, who is currently involved in the Phoenix mission--studied the presence of hydrogen peroxide, an oxidizer found during the Viking mission. The researchers highlighted a theory put forward in 2007 that states that a strong oxidizer found on Mars could have a "biological origin." Hydrogen peroxide is a great sterilizer on Earth, but on Mars it has nice properties if its mixed with water: it serves as an anti-freeze, it attracts water from atmosphere and it breaks down, producing oxygen. An enterprising extreme-ophile could cope with the increasingly dry Martian atmosphere by adapting to hydrogen peroxide.

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The researchers published a baseline for "an unbiased test for chemical versus biological responses, which can be applied at the time the Phoenix lander transmits its first results from the Martian surface." The lander has no dedicated equipment to discover biological materials­--this is as close as they could get. A co-author of the Astrobiology paper, Washington State University's Dirk Schulze-Makuch, explained to PM that the peaks and valleys in the thermal profile of the material heated inside TEGA can yield clues to the sample's compounds. "It is not clear cut, but it's the best we can do with TEGA. It's not built for this," he says. "The instrument is not as sensitive as originally planned, either."

But what about perchlorate? Could some organisms make metabolic use of the stuff? "Perchlorate is not an ideal thing for life, but there are organisms that degrade it," notes Schulze-Makuch.

Indeed, some species of bacteria are able to respire using perchlorate, using enzymes to break it down into chloride and oxygen, according to research done in 1999 in the Netherlands. More recent research has focused on using microbes like Dechloromonas aromatica to clean perchlorate pollutants found in groundwater.

Despite this theory, Martian life's best hope still remains in the fact that the planet is large and geologically diverse. NASA's probes have literally just begun scraping the surface. With the presence of water confirmed, the chance that life exists there also increases--and the extension of the Phoenix mission will keep them looking "I'd be puzzled if Mars were completely sterile," says Schulze-Makuch. "Once life got entrenched, there would be some way for life to sustain itself in ecological niches."

Soil samples taken from "Snow White" trench, shown here on July 8, 2008, were found to contain the highly oxidizing substance perchlorate after analysis in the Phoenix Mars Lander's Wet Chemistry Laboratory. (Photograph by NASA/JPL-Caltech/University of Arizona/Texas A&M University)

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